CN112689958A

CN112689958A - Method for reducing electromagnetic interference generated when transistor is placed in on-state

Info

Publication number: CN112689958A
Application number: CN201980058698.3A
Authority: CN
Inventors: J·卡纳沃; M·恩斯特
Original assignee: Vitesco Technologies GmbH
Current assignee: Vitesco Technologies GmbH
Priority date: 2018-07-10
Filing date: 2019-07-09
Publication date: 2021-04-20
Also published as: FR3083933B1; US11462996B2; FR3083933A1; WO2020020631A1; US20210359596A1

Abstract

The present invention is directed to a method for reducing electromagnetic interference generated when a transistor for switching a quasi-resonant dc-to-dc voltage converter is placed in a conducting state. The method comprises the following steps: initially, the transistor is controlled (E1) by the control module, based on a first control current, to be in a conducting state, the drive module is controlled such that it switches the transistor into a blocking state at a first time, a duration counter is triggered (E2) from the first time, and, if the counter reaches a predetermined duration threshold, the transistor is controlled (E3) by the drive module, based on a second control current, the intensity of which is smaller than the intensity of the first control current, to be in a conducting state.

Description

Method for reducing electromagnetic interference generated when transistor is placed in on-state

Technical Field

The present invention relates to the field of dc-to-dc voltage converters, and more particularly to a method for reducing electromagnetic interference generated when transistors used for switching quasi-resonant dc-to-dc voltage converters are placed in a conducting state.

Background

A direct current to direct current (also referred to as DCDC) voltage converter enables to convert an input voltage (e.g. 12V) provided by the feeding battery into a higher output voltage (e.g. 65V) or vice versa. The principle consists in charging the coil with a current and periodically switching off the current by means of a switch, in particular a transistor of the MOS type, for example.

In such a solution, the alternation of putting the switch in the conducting state and in the blocking state generates a loss called "switching loss". More precisely, when the transistor is put in the conducting state (known to those skilled in the art as being put "ON"), these losses occur when current is still flowing in the coil and when the transistor has a positive voltage across it, the losses increasing with the intensity of the current flowing in the coil and the transistor and with the voltage across the transistor. However, it is important to suppress these losses, since they can significantly reduce the efficiency of the converter.

One solution that enables the reduction of the switching losses, called "quasi-resonant" DCDC converter, consists in synchronizing the triggering of the moment at which the transistor is placed in the conducting state with a time interval (called "resonant time interval") during which the current intensity flowing in the coil is zero or negative (i.e. flows in the opposite direction) and the voltage across the transistor is minimal (or better, zero or negative). To this end, the converter includes a resonant capacitor installed between the drain and source of the transistor and a gate resistor connected to the gate of the transistor.

However, establishing the quasi-resonant state requires a delay, for example, when the converter is turned on after an interruption. Thus, when the transistor is first switched to a conducting state when it is put on, but the converter is not yet in the quasi-resonant mode, the input voltage discharges into the transistor and the resonant capacitor and causes emission of radiation by the transistor, which then acts like an antenna. The smaller the value of the gate resistance, e.g. about 4 ohms, the faster the discharge to ensure a fast discharge of the coil, thereby enabling a shorter time to put the transistor in the on-state. The effect of these disturbances is the risk of exceeding the relevant limits of electromagnetic emissions desired for such converters.

In order to remedy this drawback at least partially, a known solution consists in: instead of a single gate resistor, two parallel gate resistors with different values are used, the smaller of which is connected in series with a diode that passes only the current from the transistor gate. Thus, the current that puts the transistor in the on-state flows through the gate resistance of large value, while the current from the gate of the transistor flows in the gate resistance of small value and the diode when the transistor is switched to the off-state (discharging). Thereby, since the current that puts the transistor in the on-state is significantly smaller than the current that puts the transistor in the off-state, the current that flows in the transistor when the converter is put on is smaller, which reduces radiated emissions and electromagnetic interference. However, a small current value increases the time for putting the transistor in the conducting state, which may create a lag such that the transistor is put in the conducting state no longer coincides with the resonance time interval during which the current intensity flowing in the coil is zero or negative and the voltage across the transistor is minimal, such lag then possibly also causing electromagnetic interference.

Therefore, there is a need for a simple, fast, reliable, cost-effective and effective solution to enable electromagnetic interference to be limited.

Disclosure of Invention

To this end, the invention firstly aims at a method for reducing electromagnetic interference generated when a transistor for switching a quasi-resonant dc-to-dc voltage converter is placed in a conducting state, said converter comprising a control module, an induction coil, a field effect transistor and a drive module, the drive module being fed with a current supplied by a feed, said transistor comprising a drain, a source and a gate, said gate being connected to the drive module, the control module being configured to control the drive module so that said drive module manipulates the transistor, based on the manipulated current, in the conducting state in which the current is conducted between the drain and the source, or in a blocking state in which the current between the drain and the source is blocked, said method being noteworthy in that the drive module comprises a duration counter, said method comprising the steps of:

initially steering the transistor in a conducting state based on a first steering current, controlling the driver module by the control module such that the driver module switches the transistor into a blocking state at a first time,

triggering a duration counter from the first time instant,

if the counter reaches the preset duration threshold, the transistor is controlled to be in a conducting state through the driving module based on a second control current, and the intensity of the second control current is smaller than that of the first control current.

The expression "to manipulate the transistor in a conductive state based on the second manipulation current" means a next manipulation (or a next manipulation) of the transistor.

The method according to the invention makes it possible to reduce the intensity of the manipulation current of the transistor gate during the transient period before the converter is in a steady state reaching its quasi-resonance. This makes it possible in particular to avoid the transistor being operated with high currents, so that it is prevented from generating electromagnetic interference, without overheating as a result (which may be caused by frequent slow switching).

In contrast, if the counter has not reached the predetermined duration threshold, the (next) control current level is not changed.

Preferably, the predetermined duration threshold is between 10 and 50 μ s.

Still preferably, the intensity of the manipulation current of the transistor is reduced by about 75% to 90% of its initial value. The initial value is equal to the current strength of the transistor gate provided by the feed in a nominal case where the converter operates in the quasi-resonant mode.

According to an aspect of the invention, the intensity of the steering current is kept at its nominal value (i.e. using the first steering current) if the counter has not reached the predetermined duration threshold.

The invention also relates to a quasi-resonant dc-dc voltage converter for a motor vehicle, said converter comprising a control module, an induction coil, a field effect transistor and a drive module, the drive module being fed with a current provided by a feed, said transistor comprising a drain, a source and a gate, said gate being connected to the drive module, the control module being configured to control the drive module so that said drive module manipulates the transistor, based on the manipulated current, in a conducting state in which the current is conducted between the drain and the source, or in a blocking state in which the current between the drain and the source is blocked, said converter being noteworthy in that the drive module comprises a duration counter, the converter being configured to:

initially steering the transistor in a conducting state based on a first steering current, controlling the driver module such that the driver module switches the transistor into a blocking state at a first time,

triggering a duration counter from the first time instant,

when the counter reaches a predetermined duration threshold, the transistor is controlled to be in a conducting state based on a second control current, and the intensity of the second control current is smaller than that of the first control current.

Preferably, the converter is configured to reduce the intensity of the manipulation current of the transistor in its on-state until the next time said transistor is put in the blocking state.

In one embodiment, the drive module comprises a first switch and a second switch connected in series via an intermediate point, the first switch being connected on the one hand to the feed and on the other hand to the intermediate point, and the second switch being connected on the one hand to the intermediate point and on the other hand to ground.

Preferably, the first switch is a transistor for placing the field effect transistor in a conducting state (placed on), and the second switch is a transistor for placing the field effect transistor in a blocking state.

According to an aspect of the invention, the driving module further comprises: a third switch; a first actuator (driver) configured to switch the first switch; a second actuator configured to switch the second switch; and a driving unit for driving the third switch, configured to switch the third switch.

In a preferred embodiment, the drive unit comprises a counter, two NOT (NOT in english) type logic gates, two AND (ET AND in english) type logic gates, AND a logic flip-flop of the "RS-Q" type, for example.

Preferably, the driving module comprises a current measuring unit.

Finally, the invention relates to a motor vehicle comprising a converter as described above.

Drawings

Other features and advantages of the invention will become apparent during the following description, which refers to the accompanying drawings given by way of non-limiting example, in which similar objects are given the same reference numerals.

Fig. 1 shows an embodiment of a converter according to the invention.

Fig. 2 shows an embodiment of the method according to the invention.

Detailed Description

Fig. 1 shows an example of a converter 1 according to the invention. The converter 1 is intended to be installed in a motor vehicle, for example to provide an output voltage enabling control of the fuel injectors 2. The converter 1 is a quasi-resonant dc-dc voltage converter 1.

In the example described below, but without limitation, the converter 1 is a boost (boost) converter 1, which enables recharging of a capacitance, called "intermediate capacitance" Cint, to provide the energy required to activate the fuel injectors 2.

The converter 1 converts an input voltage Vin (input current I) to be supplied from a battery of the vehicle_L) Into the output voltages Vout applied across the intermediate capacitor Cint, these voltages being measured with respect to the ground line M.

The converter 1 comprises a control module 10, an induction coil 20, a field effect transistor 30 and a drive module 40.

The induction coil 20 is mounted at the input end of the circuit so as to be in current I when input_LWhich is charged while flowing through the induction coil 20.

The diode DI is installed between the induction coil 20 and the high terminal of the intermediate capacitor Cint, which corresponds to the output terminal of the converter 1 connected to the injector 2. The diode DI conducts from the inductor coil 20 to the intermediate capacitor Cint but blocks from the intermediate capacitor Cint to the inductor coil 20 to prevent the intermediate capacitor Cint from discharging into the converter 1.

The transistor 30 comprises a drain D, a source S and a gate G connected to the driving module 40, so that the driving module 40 manipulates the transistor 30 in a conducting state, in which a current is conducted between the drain D and the source S, or in a blocking state, in which a current is blocked between the drain D and the source S. The source S is connected to ground M and the gate G is connected to the driving module 40 via a gate resistor Rg. The capacitor Cres is connected in parallel with the transistor 30 between the drain D and the source S to quasi-resonate the converter 1.

The voltage measured at the drain D when the transistor 30 is turned off takes the following form: the square wave is then a damped sinusoidal oscillation centered around the input voltage of the converter 1 and characterized by its period.

The control module 10 is configured to send a control signal to the driving module 40, so that the driving module 40 controls the gate G of the transistor 30, so that the transistor 30 is switched to the on-state or the off-state. In other words, the driving module 40 is configured to generate a steering current for steering the gate G of the transistor 30 when being steered by the control module 10. Preferably, the steering signal originating from the control module 10 is a pulse binary type signal and enables the drive module 40 to know whether the transistor 30 should be steered to the on state (pulse 0= >1= > 0).

The drive module 40 is configured to: the transistor 30 is initially in the conducting state, the transistor 30 is controlled to be in the blocking state at a first moment, the duration counter 460 is triggered from the first moment, the control current of the transistor 30 is generated at a second moment to switch the transistor 30 to the conducting state, the duration counter 460 is stopped at the second moment, and if the duration elapsed between the first moment and the second moment is greater than a predetermined duration threshold, the intensity of the control current of the transistor 30 in its conducting state is reduced until the transistor 30 is placed in the blocking state next time.

For this purpose, in the embodiment shown in fig. 2, the drive module 40 comprises a first actuator 400, a second actuator 410, a first switch 420, a second switch 430, a third switch 440, a drive unit 445 for the third switch 440, and a current measuring unit 450.

The first switch 420 and the second switch 430 are connected in series via an intermediate point P1. The first switch 420 is connected on the one hand to the feed ALIM and on the other hand to said intermediate point P1. The second switch 430 is connected on the one hand to the intermediate point P1 and on the other hand to the earth line M.

Preferably, the first switch 420 is a transistor for placing the field-effect transistor 30 in a conducting state (placed on), and the second switch 430 is a transistor for placing the field-effect transistor 30 in a blocking state. Preferably, third switch 440 is not fixed and enables the placed-on current to be reduced by closing a negative feedback loop of the placed-on current.

The first actuator 400 is configured to switch the first switch 430 between a closed position (on state) in which current is allowed to pass and an open position (off state) in which current is inhibited from passing.

Likewise, the second actuator 410 is configured to switch the second switch 430 between a closed position (on state) that allows current to pass and an open position (off state) that inhibits current from passing.

The driving unit 445 for driving the third switch 440 is configured to: when the first switch 420 controls the transistor 30 to be in a conducting state, the third switch 440 is switched to enable the current flowing through the first switch 420 to be regulated.

In the preferred embodiment shown in fig. 1, the driving unit 445 includes a counter 460, a first not-type logic gate 470, a second not-type logic gate 475, a first and-type logic gate 480, a second and-type logic gate 485, and an "RS-Q" type logic flip-flop 490.

The current measuring unit 450 enables to measure the current flowing in the third switch 440 when the third switch 440 is closed (on-state).

The first actuator 400 comprises a first input receiving the steering signal from the control module 10 and a second input receiving from the current measurement unit 450 a measure of the current flowing in the third switch 440 when the third switch 440 is closed (conductive state), in particular when it is placed in a conductive state, so that the first actuator 400 reduces the intensity of the current flowing through the first switch 420 when the first switch 420 steers the transistor 30 in the conductive state. The output of the first actuator 400 enables manipulation of the first switch 420 in an open (blocking state) or closed (conducting state).

The second exciter 410 is an inverter type exciter. The second actuator 410 receives the manipulation signal provided by the control module 10 and complements it to manipulate the second switch 430.

The first not-type logic gate 470 allows the counter 460 to toggle when the manipulation signal from the control module 10 has a value of 0 (i.e., zero).

Accordingly, when the first and

second actuators

400 and 410 receive the same manipulation signal from the control module 10, they simultaneously open or close the first and

second switches

420 and 430 to manipulate the transistor 30 in a conductive state or a blocking state. More precisely, when the control module 10 transmits the received control signal with a binary value 1, the first actuator 400 controls the first switch 420 to be closed, while the second actuator 410 controls the second switch 430 to be open. In this case, the current flowing in the first switch 420 and the gate resistance Rg manipulates the gate G of the transistor 30 so that the connection between the drain D and the source S of the transistor 30 is turned on (the transistor 30 is in a conductive state). Conversely, when the control module 10 transmits the received manipulation signal with a binary value of 0, the first actuator 400 manipulates the first switch 420 to be open, and the second actuator 410 manipulates the second switch 430 to be closed. In this case, the voltage of the gate G of the transistor 30 drops, and a discharge current flows through the gate resistance Rg and the second switch 420. The drop of the gate G voltage below the conduction threshold of the transistor 30 cuts off the connection between the drain D and the source S of the transistor 30, so that the current flowing between said drain D and said source S is also cut off (the transistor 30 is in the blocking state).

The counter 460 includes a first input, a second input, and an output. The counter 460 is triggered when a binary signal of value 1 is received at the first input. When a binary signal having a value of 1 is received at the second input (commonly referred to as "enable"), counter 460 is reset to zero. A binary 1 value signal is generated at the output when the counter 460 reaches the predetermined duration threshold, i.e. when the counter 460 has been triggered since a duration at least equal to the predetermined duration threshold and has not been reset to zero (by its input usually referred to as "reset").

The predetermined duration threshold is selected to distinguish between transient and steady state operation of the quasi-resonant converter 1. In fact, when the converter 1 is activated after a rest period, for example when the vehicle is being contacted from the ignition key, the converter 1 requires an initial period, called "transient period", before becoming quasi-resonant. During this period the time that elapses between the transistor 30 becoming the blocking state and the subsequent transistor 30 becoming the conducting state is relatively long, while it is shorter in the steady state where the converter 1 is quasi-resonant. However, it is during this transient that a significant amount of electromagnetic interference may be generated. The predetermined duration threshold is then set such that transients are distinguished from steady states. For example, the predetermined duration threshold may be between 5 and 50 μ s.

An implementation example of the circuit of fig. 1 will now be described with reference to fig. 2.

The transistor 30 is initially in a conducting state, which is operated by a first operating current provided by the regulating voltage (in this case the supply voltage ALIM).

First, the control module 10 controls the driving module 40 at step E1 to make the driving module 40 switch the transistor 30 to the blocking state. More precisely, the control module 10 sends the control signal with a binary value 0, so that the transistor 30 switches to the blocking state. The control signal is received by the first driver 400 and the second driver 410 at the same time, the first driver 400 then controls the first transistor 420 to be turned off (the value of the binary signal is 0), and the second driver 410 then controls the second switch 430 to be turned on (the value of the complemented binary signal is 1), so that the transistor 30 is switched to the blocking state at the first time.

In step E2, the control signal complemented by the first not-type logic gate 470 to a value of 1 also triggers the counter 460 at said first moment. When the counter 460 receives a binary value of 1 at its input that is reset to 0, the counter 460 will then reset to zero.

If the duration measured by the counter 460 reaches the predetermined duration threshold before the control module 10 transmits the manipulation signal with binary value 1 (i.e., if the counter has not been reset to zero at the elapse of a duration equal to the predetermined duration threshold), the counter 460 generates a signal with binary value 1 and transmits the signal through the first and-type logic gate 480 and the logic flip-flop 490 to manipulate the third switch 440 to be closed.

Thanks to the negative feedback of the current measurement value of the current measurement unit 450 on the second input of the first actuator 400 (comparing this input with an internal reference within said first actuator 400, which internal reference corresponds to a smaller current), this results in limiting the intensity of the current flowing in the first switch 420 to a smaller value, preferably 75% to 90% smaller than the nominal value.

Therefore, in step E3, the driving module 40 controls the transistor 30 to be in a conductive state based on the manipulation current whose intensity is limited to a predetermined value smaller than that of the first manipulation current, thanks to the negative feedback of the measurement of the current measuring unit 450 to the first actuator 400 through the third switch 440.

Conversely, if the duration measured by the counter has not reached the predetermined duration threshold while the control module 10 transmits the manipulation signal with a binary value of 1 (step E1), the third switch 440 does not switch to the conductive state because the logic flip-flop 490 is set to zero by the binary value of 1 from the second and-type logic gate 485. The intensity of the current used to place the first switch 420 in the on state (on) is then not limited and will remain at its high initial value, e.g., about 100mA to 1A.

It should be noted that, instead of the logic flip-flop 190, a delay circuit that enables prevention of simultaneous switching of signals (like the RS-type logic flip-flop 190) may be used.

The present invention thus advantageously enables a reduction in electromagnetic interference that would normally be generated by placing transistor 30 in a conducting state based on the nominal current of transistor 30.

Claims

1. Method for reducing electromagnetic interference generated when a transistor (30) for switching a quasi-resonant dc-to-dc voltage converter (1) is placed in a conducting state, said converter (1) comprising a control module (10), an induction coil (20), a field effect transistor (30) and a drive module (40), the drive module (40) being fed with a current provided by a feed (ALIM), said transistor (30) comprising a drain (D), a source (S) and a gate (G), said gate (G) being connected to the drive module (40), the control module (10) being configured to control the drive module (40) such that said drive module (40) manipulates the transistor (30) in a conducting state, in which the current is conducting between the drain (D) and the source (S), or in a blocking state, in which the current between the drain (D) and the source (S) is blocked, based on a manipulation current, the method is characterized in that the drive module (40) comprises a duration counter (460), the method comprising the steps of:

initially controlling (E1) the driver module (40) by means of the control module (10) such that the driver module (40) switches the transistor (30) into the blocking state at a first time instant on the basis of the first control current controlling the transistor (30) into the conducting state,

triggering (E2) a duration counter (460) starting from the first time,

-if the counter (460) reaches the predetermined duration threshold, steering (E3), by the driving module (40), the transistor (30) in a conducting state based on a second steering current, the intensity of the second steering current being smaller than the intensity of the first steering current.

2. The method according to claim 1, wherein the predetermined duration threshold is between 10 and 50 μ s.

3. The method according to any of the preceding claims, wherein the reduction in the intensity of the steering current of the transistor (30) is about 75-90%.

4. Quasi-resonant DC-to-DC voltage converter (1) for a motor vehicle, said converter (1) comprising a control module (10), an induction coil (20), a field effect transistor (30) and a drive module (40), the drive module (40) being fed with a current provided by a feed (ALIM), said transistor (30) comprising a drain (D), a source (S) and a gate (G), said gate (G) being connected to the drive module (40), the control module (10) being configured to control the drive module (40) so that said drive module (40) manipulates the transistor (30) on the basis of a manipulation current in a conducting state in which the current is conducting between the drain (D) and the source (S) or in a blocking state in which the current between the drain (D) and the source (S) is blocked, said converter (1) being characterized in that, the drive module (40) comprises a duration counter (460), the converter (1) being configured to:

initially based on the first steering current steering the transistor (30) in a conducting state, controlling the driver module (40) such that the driver module (40) switches the transistor (30) into a blocking state at a first moment in time,

triggering a duration counter (460) from the first time instant,

when the counter (460) reaches the predetermined duration threshold, the second control current has a smaller intensity than the first control current based on the second control current controlling the transistor (30) being in the conducting state.

5. The converter (1) according to the preceding claim, wherein the converter (1) is configured to reduce the intensity of the steering current of the transistor (30) in the on-state of the transistor (30) until the next time the transistor (30) is placed in the blocking state.

6. The converter (1) according to the preceding claim, wherein the driving module (40) comprises a first switch (420) and a second switch (430) connected in series via an intermediate point (P1), the first switch (420) being connected on the one hand to the feed (ALIM) and on the other hand to the intermediate point (P1), the second switch (430) being connected on the one hand to the intermediate point (P1) and on the other hand to ground (M).

7. The converter (1) according to the preceding claim, wherein the first switch (420) is a transistor for placing the field effect transistor (30) in a conducting state and the second switch (430) is a transistor for placing the field effect transistor (30) in a blocking state.

8. The converter (1) of the preceding claim, wherein the drive module (40) further comprises: a third switch (440); a first actuator (400) configured to switch a first switch (420); a second actuator (410) configured to switch a second switch (430); a driving unit (445) for driving a third switch (440), configured to switch the third switch (440); and a current measuring unit (450).

9. Converter (1) according to the preceding claim, wherein the driving unit (445) comprises a counter (460), two not-type logic gates (470, 475), two and-type logic gates (480, 485), and a logic flip-flop (490).

10. Motor vehicle comprising a converter (1) according to one of claims 4 to 9.